In modern commercial aircraft, more and more frequently winglets are used, whose purpose it is to reduce the induced resistance of the wing and to increase the Ca/Cw ratio and thus to reduce the resistance and the fuel consumption.
Generally speaking, winglets are rigid constructions at the end of the wings, comprising an aerodynamic profile that is positioned at three specified angles to the direction of airflow. The alignment of the winglets is designed for the longest flight phase, namely for cruising. Moreover, the maximum effect of the winglets is achieved during cruising. This means that winglets are designed for high Mach numbers Ma=0.8 and approx. 10,000 m cruising altitude with corresponding air pressure, density and temperature. The flight phases of climbing flight, approach to landing, takeoff and landing are not taken into account in the above.
U.S. Pat. No. 5,988,563 and US 2004/0000619 A1 each disclose a foldable winglet that may rotate in relation to the wing on an attachment axis and that during flight may be moved between a folded-in and a folded-out position.
Since the aerodynamic load on the winglets is above all extremely high at a large angle of yaw and during lateral gusts, the winglets must be designed so as to be enormously robust for these load cases. Due to the load introduction from the winglet to the wing element, the wing element must then also be designed so as to be correspondingly robust.
WO 03/00547 discloses that loads resulting from vertical maneuvers may be reduced by local control surfaces on the winglet, in that by opening these control surfaces the aerodynamic load is reduced.